With economic development and the improvement of living standard people pay more and more attention to white, clean, healthy tooth. Tooth can be pigmented due to various reasons in daily life. Dental fluorosis is caused by high level of fluoride in drinking water, tetracycline pigmented tooth is caused by excessive intake of tetracycline antibiotics during childhood. The other factors in daily life, for example, cigarette, tea, coffee, vinegar etc. can also pigment tooth. Thus tooth-bleaching and other cosmetic treatment has become a hot topic in dentistry.
Traditionally 33% oxygen peroxide was used to treat pigmented tooth. It is first applied to pigmented tooth surface, then the tooth is exposed to strong light, which can impel oxygen peroxide to decompose and release oxygen that have tooth-bleaching effects. But its application is limited because of its strong erosive effect. Haywood, an American dentist, et al, found in 1989 that carbamide peroxide can bleach tooth through releasing oxygen and its effective concentration of 10% has no erosive effect on gingiva. This finding was soon put to practical use and three generations of tooth-whitening products were produced. The first was 10% carbamide peroxide solution which could be used by dentist only. It was used by dipping some solution with a small cotton ball, then apply it to and maintain it on tooth surface for a period of time. Catalyzer, which can catalyze carbamide peroxide to decompose into water and carbamide and release oxygen, could be added at this time to enhance the reaction. The second was carbamide peroxide gel, the example product was Opalescence produced by an American company Ultradent. It was improved in its application method. A plastic denture was made according to the dental impression of the patient. The patient was asked to put the denture, with the gel in it, into mouth before going to bed and take it off in the morning. In this way, the reaction time of carbamide peroxide on tooth surface was extended. This was called "night tooth-bleaching technique". The improvement in the third generation was also its way of application. A specially-made soft tray, which fitted well with the patient's denture, was used to load tooth-bleaching agent. It was put into mouth for 1 hour every day, 7 days for a course of treatment. It usually took several treatment courses to see the effect.
It can be seen that the effectiveness of carbamide peroxide lies in the duration of its action on tooth surface. The above mentioned products used complicated appliances to extend its reaction time, which were complicate in operation and high in cost. An easy to use, low in cost tooth-whitening agent is badly needed at present.